The grid designer that replaced the old GridBagCustomizer in NetBeans 6.9 doesn't visualize insets in any way. Hence, it is sometimes hard to find out whether some component doesn't occupy the whole area of its cells beacuse it has some insets assigned or just because the columns/rows are padded.
Similarly, it would be nice to provide some visualization of components with gridwidth/gridheight/gridx/gridy set to REMAINDER or RELATIVE.